Touch systems are well known in the art and typically include a panel having a touch surface on which contacts are made using a pointer in order to generate user input. Pointer contacts with the touch surface are detected and are used to generate corresponding output depending on areas of the touch surface where the contacts are made. There are basically two general types of touch systems available and they can be broadly classified as “active” touch systems and “passive” touch systems.
Active touch systems allow a user to generate user input by contacting the touch surface with a special pointer that usually requires some form of on-board power source, typically batteries. The special pointer emits signals such as infrared light, visible light, ultrasonic frequencies, electromagnetic frequencies, etc. that activate the touch system.
Passive touch systems allow a user to generate user input by contacting the touch surface with a passive pointer and do not require the use of a special pointer in order to activate the touch system. A passive pointer can be a finger, a cylinder of some material, or any suitable object that can be used to contact the touch surface.
Passive touch systems provide advantages over active touch systems in that any suitable pointing device, including a user's finger, can be used as a pointer to contact the touch surface. As a result, user input can easily be generated. Also, since special active pointers are not necessary in passive touch systems, battery power levels and/or pointer damage, theft, or misplacement are of no or little concern to users.
International PCT Application No. PCT/CA01/00980 filed on Jul. 5, 2001 and published under No. WO 02/03316 on Jan. 10, 2002, assigned to SMART Technologies Inc., assignee of the present invention, discloses a camera-based touch system comprising a touch screen that includes a passive touch surface on which a computer-generated image is presented. A rectangular bezel or frame surrounds the touch surface and supports digital cameras at its corners. The digital cameras have overlapping fields of view that encompass and look across the touch surface. The digital cameras acquire images looking across the touch surface from different locations and generate image data. Images acquired by the cameras are processed by digital signal processors to determine if a pointer exists in the captured images. When it is determined that a pointer exists in the captured images, the digital signal processors convey pointer characteristic data to a master controller, which in turn processes the pointer characteristic data to determine the location of the pointer relative to the touch surface using triangulation. The pointer location data is conveyed to a computer executing one or more application programs. The computer uses the pointer location data to update the computer-generated image that is presented on the touch surface. Pointer contacts on the touch surface can therefore be recorded as writing or drawing or used to control execution of software application programs executed by the computer.
Although the above touch system works extremely well, the use of four digital cameras and associated digital signal processors to capture and process images makes the touch system hardware-intensive and therefore, increases the costs of manufacture. This of course translates into higher costs to consumers. In some environments where expense is a primary concern, less expensive touch systems are desired.
Camera-based touch systems having reduced hardware have been considered. For example, U.S. Pat. No. 5,484,966 to Segen discloses an apparatus for determining the location of an object in an active area of a first plane. The apparatus includes a pair of mirrors extending along different sides of the active area and oriented so that their planes are substantially perpendicular to the plane of the active area. The mirrors form a 90° angle with respect to one another and intersect at a corner of the active area that is diagonally opposite a detecting device. The detecting device includes a mirror and a CCD sensor and looks across the plane of the active area. A processor communicates with the detecting device and receives image data from the CCD sensor.
When a stylus is placed in the active area, the detecting device sees the stylus directly as well as images of the stylus reflected by the mirrors. Thus, images captured by the detecting device include the stylus and one or more stylus reflections. The captured images are processed by the processor to detect the stylus and stylus reflections in the captured images and to calculate the location of the stylus in the active area using triangulation.
Although the Segan apparatus reduces hardware requirements since only one detecting device and processor are used, problems exist in that the line of sight of the detecting device to some areas of the active area may be impeded by a user's hand and/or forearm if the user rests their hand and/or forearm in the active area during writing. This problem is further exaggerated in the case of some left-handed users who tend to curl their arms to the left of and over the area in which they are writing and rest their forearms and hands in the active area.
The above writing scenario is illustrated in FIG. 1 which shows an apparatus 10 similar to that disclosed by Segan. The apparatus 10 includes a touch surface 12 and an imaging device 14 positioned at one corner of the touch surface. The imaging device 14 looks across the touch surface 12. Mirrors 16 and 18 border two sides of the touch surface 12 and intersect at the corner of the touch surface diagonally opposite the imaging device. A pointer P held by a user is in contact with the touch surface 12 during writing. In this writing scenario, during pointer contact on the touch surface, the user's forearm F and hand H are also in contact with the touch surface 12. As will be appreciated, if the user contacts the touch surface 12 using a pointer P in this manner, problems in detecting the location of pointer contact on the touch surface 12 arise. This is due to the fact that the line of sight of the imaging device 14 directly to the pointer P and the line of sight of the imaging device to two of the three pointer images appearing in the mirrors 16 and 18 are blocked by the user's forearm F and hand H. As a result, the imaging device 14 is unable to acquire sufficient pointer data to enable the location of pointer contact on the touch surface 12 to be calculated via triangulation. As will be appreciated, improvements in touch systems of this nature are desired.
It is therefore an object of the present invention to provide a novel apparatus for detecting a pointer within a region of interest.